Method for manufacturing carbon fibers and method for manufacturing electron emitting device using the same, method for manufacturing display, and ink for producing catalyst for use in these methods

ABSTRACT

To provide an ink for producing a catalyst capable of stably forming metal particles which act as catalysts suitable for growth of carbon fibers by applying them onto a substrate.  
     A solution containing a metal organic compound containing any one metal of Pd, Fe, Co and Ni and a water-soluble polymer compound is formed by using water or an organic solvent as a main solvent.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for manufacturingcarbon fibers and method for manufacturing an electron emitting deviceusing the carbon fibers, method for manufacturing a display using theelectron emitting device, and an ink for producing a catalyst for use inthese methods.

[0003] 2. Description of the Related Art

[0004] A field emission-type (FE-type) electron emitting device, whereinelectrons are emitted from a metal surface by applying a strong electricfield of 10⁶ V/cm or more toward a metal, has attracted attention as oneof cold cathode electron-emitting devices. The practical use of theFE-type cold cathode electron-emitting device may enable realization ofan emissive thin display device and contribute reduction of powerconsumption and weight saving.

[0005]FIG. 7 shows the structure of a vertical FE-type electron emittingdevice. In the Figure, 71 refers to a substrate; 72 to a extractionelectrode (gate electrode); 73 to a cathode electrode; 74 to aninsulating layer; 75 to an emitter. 76 to a positive electrode (anode)and 77 to a shape of an electron beam irradiated to a positive electrode76. It has a structure (hereinafter referred to as Spindt type) whereinan opening is formed in a stack of the insulating layer 74 and theextraction electrode 72 arranged on the cathode electrode 73 and aconical emitter 75 is arranged in the opening (for example, see C. A.Spindt, “Physical Properties of thin-film field emission cathodes withmolybdenum cones”, J. Appl. Phys., 47, 5248 (1976)).

[0006] In addition, as an example of a lateral FE-type electron emittingdevice, there may be mentioned a device wherein an emitter having anacute tip and a extraction electrode extracting (drawing) out anelectron from the emitter tip are formed parallel to a substrate and acollector (called as an anode in the present case) is constituted in theorthogonal direction toward the direction that the extraction electrodeand the emitter face each other.

[0007] Furthermore, an electron emitting device using fibrous carbon hasbeen proposed (for example, see Japanese Patent Application Laid-OpenNo. H08-115652, Japanese Patent Application Laid-Open No. 2000-223005,and European Patent Laid-Open No. 1022763).

[0008] As a method for manufacturing carbon fibers on the substrate,there is a method for manufacturing the same by disposing catalystparticles comprising a metal on the substrate and thermally decomposinga carbon compound such as a hydrocarbon using the catalyst particles asnuclei. As a method for disposing said catalyst particles onto thesubstrate, there is known a method of directly forming a catalyst metalby a depositing technology, e.g., a sputtering method. Also, a method ofusing a metal complex (for example, see Japanese Patent No. 2903290) anda method of using a metal nitrate or a metal chloride have been reported(for example, see Japanese Patent Application Laid-Open No. H03-260119)

SUMMARY OF THE INVENTION

[0009] A method of applying a solution of a metal compound dissolved ina solvent as a method for arranging a metal as a catalyst on a substrateis an advantageous process in the case of, for example, forming anelectronic device using carbon fibers on a substrate having a large areasince the process does not require a vacuum apparatus as compared with amethod of direct deposition such as a sputtering method.

[0010] However, in the case of the application as a solution onto thesubstrate, a problem that particles are not stably formed after bakingand reduction has arisen in the method of applying a solution in whichonly a metal compound is dissolved. Moreover, in the case of baking aninorganic salt such as a nitrate or a chloride, there is a possibilityof generating a corrosive gas to damage the apparatus and the like.

[0011] Therefore, there is existed a problem that it is difficult tostably form catalyst particles for growing carbon fibers by asolution-applying method.

[0012] Namely, in order to manufacture carbon fibers to be applied to anelectronic device including an electron emitting device as arepresentative, it is desired to develop a method for stably formingcatalyst particles on a substrate without requiring any complex process.

[0013] An object of the present invention is to provide a method formanufacturing carbon fibers efficiently in a good yield ratio using anink for producing a catalyst capable of stably forming metal-containingparticles on a substrate, the particles acting as a catalyst suitablefor growing the carbon fiber. Another object of the present invention isto provide a method for manufacturing an electronic device such as anelectron emitting device having the carbon fibers and a method formanufacturing a display comprising the electron emitting device.

[0014] The invention has been accomplished as a result of extensivestudies for solving the above-mentioned problem. The invention includesthe following constitutions.

[0015] According to one aspect of the present invention, there isprovided a method for manufacturing carbon fibers comprising:

[0016] a step of forming a coated film containing a metal organiccompound and a polymer compound by applying an ink for producing acatalyst comprising a solution containing at least the metal organiccompound and the polymer compound onto a substrate,

[0017] a step of forming catalyst particles comprising a metalconstituting the above metal organic compound by heating the abovecoated film, and

[0018] a step of forming carbon fibers by bringing a gas containingcarbon into contact with the above catalyst particles.

[0019] According to another aspect of the present invention, there isprovided a method for manufacturing an electron emitting devicecontaining carbon fibers connected to an electrode, comprising:

[0020] a step of forming a coated film comprising a metal organiccompound and a polymer compound by applying an ink for producing acatalyst comprising a solution containing at least the metal organiccompound and the polymer compound onto the electrode,

[0021] a step of forming catalyst particles comprising a metalconstituting the metal organic compound on the electrode by heating thecoated film, and

[0022] a step of forming carbon fibers by bringing a gas containingcarbon into contact with the above catalyst particles.

[0023] In the above method for manufacturing carbon fibers and the abovemethod for manufacturing an electron emitting device according to theinvention, the following constitutions are included as preferredembodiments.

[0024] 1) The polymer compound is a water-soluble polymer compound. Inparticular, the polymer compound is any one of polyvinyl alcohol,polyacrylic acids and polyvinylpyrrolidone.

[0025] 2) The metal constituting the metal organic compound is any oneof Pd, Fe, Co and Ni.

[0026] 3) The metal organic compound is a metal organic complex.

[0027] 4) A main solvent of the catalyst-manufacturing ink is water oran organic solvent.

[0028] 5) The step of heating the coated film is carried out in anon-oxidizing atmosphere. Alternatively, the step is carried out bybaking the coated film in an oxidizing atmosphere and then heating it ina reducing atmosphere.

[0029] 6) The gas containing carbon is a hydrocarbon gas or a mixed gasof a hydrocarbon gas with hydrogen gas.

[0030] According to a further aspect of the present invention, there isprovided an ink for producing a catalyst for growing carbon fibers,comprising at least a metal organic compound, a polymer compound and asolvent.

[0031] In the above catalyst-manufacturing ink according to theinvention, the following constitutions are included as preferredembodiments. 1) The polymer compound is a water-soluble polymercompound. In particular, the polymer compound is any one of polyvinylalcohol, polyacrylic acids and polyvinylpyrrolidone.

[0032] 2) The metal constituting the metal organic compound is any oneof Pd, Fe, Co and Ni.

[0033] 3) The metal organic compound is a metal organic complex.

[0034] 4) A main solvent of the catalyst-manufacturing ink is water oran organic solvent.

[0035] According to still another aspect of the present invention, thereis provided a method for manufacturing a display using a plurality ofelectron emitting elements, wherein the electron emitting elements aremanufactured by the method of the above second aspect of the invention.

[0036] According to the present invention, catalyst particles forgrowing carbon fibers can be stably formed by applying an ink forproducing a catalyst containing a metal organic compound and a polymercompound onto a substrate, followed by heating. An electron emittingelement grown from the catalyst particles and containing carbon fibersconnected to an electrode exhibits a satisfactory electron emittingcharacteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037]FIGS. 1A, 1B, 1C, 1D and 1E illustrate one example of the processfor manufacturing an electron emitting element of the invention.

[0038]FIGS. 2A and 2B illustrate one example of the electron emittingelement of the invention.

[0039]FIG. 3 illustrates a state at the time when the electron emittingelement of FIGS. 2A and 2B is operated.

[0040]FIG. 4 illustrates an electron emitting characteristic of theelectron emitting element according to the invention.

[0041]FIGS. 5A, 5B and 5C are schematic illustrations of structure ofcarbon nanotubes.

[0042]FIGS. 6A, 6B, 6C-1 and 6C-2 are schematic illustrations ofstructure of graphite nanofibers.

[0043]FIG. 7 illustrates a conventional vertical FE-type electronemitting element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0044] The following will describe the method for manufacturing carbonfibers and the method for manufacturing an electron emitting device asone example of electronic devices, and the catalyst-manufacturing inkfor use in these methods according to the invention with reference toEmbodiments. However, sizes, materials and shapes of the constitutingparts and a relative position thereof described below should not beconstrued to limit the scope of the invention thereto. Also, the methodfor manufacture is not limited to the steps described below.

[0045] In this invetion, the “carbon fiber” or “fiber mainly composed ofcarbon” in the present invention. includes a carbon nanotube “hollowfiber”, a graphite nanofiber (referring to a “fiber constituted bystacking graphenes in the axial direction of the fiber” or a “carbonfiber constituted by stacking a large number of graphenes having c-axiswhich is not perpendicular to the fiber axis” including a cup stacktype), a carbon nanocoil (a spiral carbon fiber), carbon nanohorn(carbon fibers wherein one end of a carbon nanotube is closed), and anamorphous carbon fiber.

[0046] Moreover, the catalyst particles comprising a metal in thepresent invention. include not only particles composed of the metalalone but also particles mainly composed of the metal.

[0047] First, there is described the method for manufacturing carbonfibers of the invention using the catalyst-manufacturing ink of theinvention.

[0048] In the method for manufacturing carbon fibers of the invention,an ink for producing a catalyst comprising a solution containing atleast a metal organic compound and a polymer compound is applied onto asubstrate.

[0049] It is to be noted that the “catalyst-manufacturing ink” in thepresent invention. means a liquid containing raw materials for formingdesired catalyst particles but conceptually does not exclude a liquidhaving a function or purpose other than the formation of catalystparticles.

[0050] In the present invention, the metal constituting the metalorganic compound contained in the catalyst-manufacturing ink ispreferably a metal selected from noble metals such as palladium,platinum, rhodium, iridium, ruthenium and osmium, and first transitionmetals such as titanium, vanadium, chromium, manganese, iron, cobalt andnickel.

[0051] As the metal organic compounds containing the above noble metals,specifically, the metal organic compounds containing palladium includepalladium acetylacetonates, palladium carboxylates such as palladiumacetate, and the like, the metal organic compounds containing platinuminclude platinum acetylacetonates, platinum carboxylates such asplatinum acetate, and the like, the metal organic compounds containingrhodinum include rhodium acetylacetonates, rhodium carboxylates such asrhodium octylate (dimer) and rhodium acetate (dimer), and the like, themetal organic compounds containing iridium include iridiumacetylacetonates and the like, the metal organic compounds containingruthenium include ruthenium acetylacetonates and the like, and the metalorganic compounds containing osmium include osmium acetylacetonates andthe like.

[0052] As the metal organic compounds containing the above firsttransition metals, specifically, the metal organic compounds containingtitanium include titanium acetylacetonates, titanium oxideacetylacetonates and the like, the metal organic compounds containingvanadium include vanadium acetylacetonates, vanadium oxideacetylacetonates and the like, the metal organic compounds containingchromium include chromium acetylacetonates, chromium carboxylates suchas chromium acetate, and the like, the metal organic compoundscontaining manganese include manganese acetylacetonates, manganesecarboxylates such as manganese acetate, manganese formate and manganesebenzoate, and the like, the metal organic compounds containing ironinclude iron acetylacetonates, iron carboxylates such as iron acetate,iron octylate, iron stearate and iron oxalate, and the like, the metalorganic compounds containing cobalt include cobalt acetylacetonates,cobalt carboxylates such as cobalt acetate, cobalt naphthenate andcobalt oxalate, and the like, the metal organic compounds containingnickel include nickel acetylacetonates, nickel carboxylates such asnickel acetate, nickel formate and nickel stearate, and the like, themetal organic compounds containing copper include copperacetylacetonates, copper carboxylates such as copper acetate and copperbenzoate, and the like. In addition, the metal organic compounds of thefirst transition metals also include metal carbonyl compounds, alkoxymetal compounds, cyclopentadienyl metal compounds and the like but thesecompounds are apt to be influenced by moisture, so that it is necessaryto use an anhydrous organic solvent or the like when the compounds areused.

[0053] The above metal organic compound containing a noble metal or afirst transition metal may be an organic complex to which a ligandcoordinates. The ligand includes a compound coordinating with an oxygen(O) atom, a compound coordinating with an nitrogen (N) atom, or thelike, but, preferred is a compound coordinating with a nitrogen (N)atom, such as amines, alcohol amines or ethylenediamines.

[0054] Among the above noble metals and first transition metals,palladium, iron, cobalt and nickel are preferably used as the metalsconstituting the metal organic compounds of the invention.

[0055] In particular, as the metal organic compounds containingpalladium, preferred are palladium acetylacetonate, palladiumcarboxylates and the like.

[0056] Moreover, the palladium carboxylates may be coordinated by anamine ligand. For example, a compound coordinated by ammonia,ethanolamine, ethylenediamine or the like is also preferred.Tetra(monoethanolamine)palladium acetate or the like is a preferredcompound for an aqueous system.

[0057] As the metal organic compounds containing iron, cobalt, ornickel, preferred are iron acetylacetonate, cobalt acetylacetonate,nickel acetylacetonate, iron alkylcarboxylates, cobaltalkylcarboxylates, nickel alkylcarboxylates and the like.

[0058] Furthermore, for carboxylates, also preferred is an amine ligand,for example, a compound coordinated by a nitrogen atom of ammonia,ethanolamine, ethylenediamine and the like. Moreover, a concentrationrange of the metal in the metal organic compound for use in the presentinvention. somewhat varies depending on the kind of the metal organiccompound to be used, but is preferably from 0.005% to 1% by weight basedon the weight of the solution (ink for producing catalyst). Too lowmetal concentration may invite too small amount of metal fine particles,and too high metal concentration tends to result in a metal film. Thus,it becomes difficult to form catalyst particles on a substrate.

[0059] Next, the polymer compound to be contained in thecatalyst-manufacturing ink will be described.

[0060] In the present invention, the catalyst particles comprising ametal (particles mainly composed of the metal) can be stably formed byapplying an ink for producing a catalyst which is a solution containinga metal organic compound and a polymer compound onto a substrate,followed by baking and reduction. This is because effects of the polymercompound have appeared at the application of the ink. The situationwhere the solvent is removed by drying after the application resemblesthe situation at an operation for recrystalization which is a method forpurifying a solid compound. This is a situation where crystals of themetal organic compound in the metal organic compound may be precipitatedon the substrate as large particles. However, since the polymer compoundis present in the solution, the metal organic compound cannot freelymove by the action of the polymer compound even when the metal organiccompound is dispersed or the solvent is dried, and thus the metalcompound remains dispersed. Therefore, discrete catalyst particles canbe formed after baking and reduction.

[0061] The polymer compound according to the invention is preferably awater-soluble polymer compound. This is because a functional group forachieving the water solubility tends to interact with the metal organiccompound and also with the substrate, and hence the functional groupmakes it easy to disperse the organic compound. As the water-solublepolymer compound, preferred are polyvinyl alcohol, polyvinylpyrrolidoneand polyacrylates. The polyvinyl alcohol for use in the presentinvention, may contain polyvinyl alcohol partially esterified. Degree ofpolymerization of the water-soluble polymer compound is preferably inthe range of 400 to 2000. When the degree of polymerization is smallerthan the range, the metal organic compound is difficult to dispersesufficiently and when the degree of polymerization is larger than therange, viscosity of the solution becomes too high, and there arises aproblem in its application. In order to disperse the metal organiccompound without resulting in too high solution viscosity, it ispreferable to use a polymer compound whose degree of polymerization isfrom 400 to 2000. The concentration of the water-soluble polymercompound for use in the present invention. is preferably from 0.01 to0.5% by weight. When the compound is used within the range, a gooddispersibility of the metal organic compound is achieved.

[0062] As the solvent for the catalyst-manufacturing ink of theinvention, either water or an organic solvent can be preferably used asa main solvent. As the organic solvent to be used as the main solvent,use can be made of a solvent such as an alcohol such as methanol,ethanol, 1-propyl alcohol, 2-propyl alcohol, 2-butanol; an aromaticsolvent such as toluene; or N-methylpyrrolidone, N,N-dimethylacetamide,N,N-dimethylformamide, dimethyl sulfoxide, or the like. These solventsmay be used solely or as a mixture of two or more of them.

[0063] Moreover, as the solvent for the ink, in an aqueous solvent, analcohol can be further added. As an alcohol to be added, use can be madeof a monohydric alcohol mentioned in the above as the main solvent or apolyhydric alcohol such as ethylene glycol, propylene glycol, diethyleneglycol glycerin and the like. The addition of such an alcohol maysometimes improve wettability.

[0064] In the method for producing carbon fibers of the invention, asthe method of applying the above catalyst-manufacturing ink onto asubstrate, a usual applying method such as spin coating, dipping, spraycoating and the like can be employed. As other applying methods, liquiddrop-applying methods including an ink-jet method such as a piezo systemor a heating and bubbling system (bubble-jet, a registered trademark) asa representative can be also employed. The ink-jet method is preferablyemployed since a desired amount can be selectively imparted to a desiredregion. By these methods, a coated film containing the metal organiccompound and the polymer compound is formed on a substrate.

[0065] Then, by heating (baking) the above coated film, catalystparticles comprising the metal constituting the metal organic compoundcontained in the ink is formed. The heating step will be describedbelow.

[0066] For the heating step of forming catalyst particles comprising themetal constituting the metal organic compound by heating the coated filmcontaining the metal organic compound and the polymer compound, a methodof conducting in a non-oxidizing atmosphere and a method of heating in areductive atmosphere after baking the coated film in an oxidizingatmosphere may be mentioned. In case where a polymer is removed, heatingin an oxidizing atmosphere is preferable.

[0067] In the method of conducting in a non-oxidizing atmosphere,catalyst particles comprising the metal constituting the metal organiccompound are formed through thermal decomposition of the metal organiccompound by heating it under vacuum at about 500° C. to 700° C.

[0068] In the method of heating in a reductive atmosphere after bakingthe coated film in an oxidizing atmosphere, catalyst particlescomprising the metal constituting the metal organic compound are formedby baking the metal organic compound at about 200° C. to 500° C.,preferably about 350° C. to convert it into corresponding metal oxideand then reducing it under a hydrogen atmosphere at about 500° C. to700° C.

[0069] After the catalyst particles are formed by heating the coatedfilm, carbon fibers are grown using the catalyst particles. Namely,carbon fibers are formed by bringing a gas containing carbon intocontact with the catalyst particles and simultaneously heating them. Inother words, the carbon fiber is grown by bringing a gas containingcarbon into contact with the catalyst particle, whose catalytic functionis being activated. Typically, the carbon fiber can be grown by bringinga gas containing carbon into contact with the catalytic particledisposed on the base member which is being heated.

[0070] As the gas containing carbon for use in the present invention, ahydrocarbon gas such as acetylene, ethylene, methane, propane orpropylene is preferably used, but the gas may be a vapor of an organicsolvent such as ethanol or acetone. Moreover, a mixed gas of the abovehydrocarbon gas with hydrogen gas is also preferably used. In the casethat the mixed gas is used, when the coated film is baked in anoxidizing atmosphere, e.g., in the air, carbon fibers can be grown in amixed gas stream of the hydrocarbon gas with hydrogen gas, withouttaking out a substrate, under a reduction treatment in a hydrogen gasstream with further flowing the hydrogen gas.

[0071]FIGS. 5A to 5C and 6A to 6C-2 show schematic illustrations ofcarbon fibers formed by decomposing a hydrocarbon gas using the abovecatalyst particles according to the invention. Each of FIGS. 5A and 6Ashows a morphologic feature observed at an optical microscope level (themagnification of up to 1000).

[0072] Each of FIGS. 5B and 6B shows a morphologic feature observed at ascanning electron microscope (SEM) level (the magnification of up to30,000) and is an enlarged view of 51 and 61 in FIGS. 5A and 6A,respectively. Each of 5C, 6C-1 and 6C-2 shows a morphologic feature ofcarbon observed at a transmission electron microscope (TEM) level (themagnification of up to 1,000,000). FIG. 5C schematically illustrates anenlarged view of 52 in FIG. 5B, FIGS. 6C-1 schematically illustrates anenlarged view of 62 in FIG. 6B, and FIGS. 6C-2 schematically illustratesan enlarged view of 63 in FIG. 6B.

[0073] As shown in FIGS. 5A to 5C, the fiber wherein the 53 has amorphologic feature of cylindrical shape (the fiber having amulti-structured cylindrical shape of graphene is called a multi-wallnanotube) is called a carbon nanotube. In particular, when a tip of thetube has an opened structure, it exhibits the lowest threshold level.

[0074] Alternatively, FIGS. 6A to 6C-2 schematically illustrate thecarbon fibers formed at a relatively low temperature similarly using acatalyst as in the case of the carbon nanotube. This type of carbonfiber (sometimes called a “graphite nanofiber”) is constituted bystacked graphenes 64 in the axis direction of the fiber.

[0075] Either carbon fiber has a threshold level for electron emissionof about 1 to 10 V/μm and has preferable characteristics as an electronemitting material. However, since the graphite nanofiber is superior inan electron emitting ability to the carbon nanotube, it is preferable toselect the graphite nanofiber for an electron emitting device havingcarbon fibers.

[0076] The following will describe an electron emitting device using thecarbon fiber obtained by the invention in detail with reference to FIGS.1A, 1B, 1C, ID, 1E, 2A and 2B.

[0077]FIG. 2A is a schematic illustration showing one example ofstructure of the electron emitting device according to the invention andFIG. 2B is a cross-sectional view at 2B-2B in FIG. 2A. FIGS. 2A and 2Bis a drawing after carbon fibers are grown using catalyst particles.

[0078] In FIGS. 1A, 1B, 1C, 1D, 1E, 2A and 2B, reference 11 denotes aninsulating substrate; reference 12 denotes second electrode (extractionelectrode (gate electrode) for. extracting electrons from the fiber, orcontrol electrode for controlling electrons emitted from the fiber);reference 13 denotes first electrode (cathode electrode); reference 14denotes a resist pattern; reference 15 denotes a conductive materiallayer; reference 16 denotes catalyst particles; reference 17 denotescarbon fibers which are materials for an emitter. Note that theconductive material layer 15 is not always necessary. In this example,the conductive material layer 15 where the first electrode 13 andcatalyst particles 16 are arranged has a stacked structure, but it issufficient for the layer to have a morphologic feature where catalystparticles 16 are exposed on the surface of the negative electrode 13.Namely, a morphologic feature where the first electrode 13 has catalystparticles 16 is also possible.

[0079] As the insulating substrate 1, an insulating substrate such assilica glass whose surface is thoroughly washed may be mentioned.

[0080] The second electrode 12 and the first electrode 13 are conductiveand are formed by a general vacuum film-forming technology such as vapordeposition, sputtering and the like, a photolithography technology orthe like. The material is desirably a heat-resistant material such ascarbon, a metal, a metal nitride or a metal carbide.

[0081] The carbon fiber 17 is a carbon fiber such as a carbon nanotubeor graphite nanofiber grown using catalyst particles 16 of FIGS. 1A to1E (namely, catalyst particles obtained by forming a coated filmcontaining a metal organic compound and a polymer compound by applyingan ink for producing a catalyst containing the metal organic compoundand the polymer compound and heating (baking) the above coated film).

[0082] The following will describe one example of the process forproducing the electron emitting element shown in FIGS. 2A and 2B withreference to FIGS. 1A to 1E.

[0083] (Step 1)

[0084] After the substrate 11 is thoroughly washed, an electrode layerhaving a thickness of 500 nm (not shown in the Figure) is first formedall over the substrate by sputtering or the like in order to form thedrawer electrode 12 and the negative electrode 13.

[0085] Next, in a photolithographic step, a resist pattern is formedusing a positive photoresist (not shown in the Figure). Then, using theabove patterned photoresist as a mask, the electrode layer is subjectedto a dry etching using Ar gas to pattern the second electrode 12 andfirst electrode (cathode electrode) 13 having a gap between theelectrodes (gap width) of 5 μm (FIG. 1A).

[0086] Hereinafter, the patterning of the thin layers and resists by aphotolithography technology, film formation, lift-off, etching, and thelike are simply referred to as “patterning”.

[0087] (Step 2)

[0088] In a photolithographic step, the resist pattern 14 is formedusing a negative photoresist to be used for successive lift-off of anupper layer (FIG. 1B).

[0089] Next, therein is formed a conductive material layer (TiN is usedtherein) wherein carbon fibers 17 are grown using catalyst particles 16.Then, the catalyst-manufacturing ink is applied therein with rotation toform a coated film containing a metal organic compound and a polymercompound and then the film is heated to form catalyst particles 16 ofthe metal (FIG. 1C). In case where a polymer is removed, the abovecoated film is preferably heated in an oxidizing atmosphere. Further,when the areas of catalyst particles to be disposed are patterned(especially, when the patterning is carried out by a wet process), it ispreferable to pattern the catalyst particles oxidized by heating thecoated film in an oxidation atmosphere and then reduce the oxidizedparticles by heating them, for example, in a reduced gas atmosphere.Thus, the loss of a material constituting the catalyst particles with apeeling agent and solvent patterning can be suppressed. According to theinvention, by adding a polymer, distance between neighboring catalystparticles can be arbitrarily controlled. Therefore, growth of carbonfibers using catalyst particles formed according to the inventionresults in control of the distance between carbon fibers. As a result,in the case that a large number of carbon fibers are grown on the firstelectrode 13 and are used as an electron emitting device, an electricfield can be sufficiently applied to the individual carbon fibers andgood electron emitting characteristics can be realized.

[0090] (Step 3)

[0091] Using a removing liquid (remover) for the resist patterned inStep 2, the conductive material layer 15 and catalyst particles 16 onthe resist are lifted off together with the resist and a pattern of theconductive material layer 15 and catalyst particles 16 is left in adesired region (FIG. 1D).

[0092] When a photosensitive material is further added to the ink forproducing catalyst or when the photosensitivity is given to a polymerincluded in the ink for producing catalyst, after coated on thesubstrate with the previously patterned conductive material layer, thedesirably patterned coated film comprising an organic compound andpolymer is formed by the conventional photolithography techniques inwhich exposure and development are carried out using a mask. Next, aheating step is carried out in a non-oxidizing atmosphere, or a heatingstep is carried out in an oxidizing atmosphere and then a heating stepis carried in a reducing atmosphere, to form catalyst particle patternon the desired areas. Although the above heating step may be carried outin a non-oxidizing atmosphere, in case where a polymer is removed,baking in an oxidizing atmosphere is preferable.

[0093] (Step 4)

[0094] Subsequently, the product is subjected to a thermal decomposition(thermal CVD) treatment in a stream of a gas containing carbon. Then,when it is observed on a scanning electron microscope, it is found thata large number of carbon fibers are formed (FIG. 1E).

[0095] The following will describe the thus manufactured electronemitting device using the carbon fibers with reference to FIGS. 3 and 4.

[0096] The device equipped with the second electrode (gate electrode) 12and the cathode electrode 13 having a gap between them of several μm, asshown in FIGS. 2A and 2B, is placed in a vacuum apparatus 38 as shown inFIG. 3 and the apparatus is thoroughly evacuated until the pressurereaches about 10⁻⁴ Pa by a vacuum evacuating apparatus 39. As shown inFIG. 3, using a high voltage source, a positive electrode (anode) 30 isprovided at a position having a height H of several mm from thesubstrate and a high voltage of several kilo volts is applied.

[0097] In this connection, a fluorescent material 31 covered with aconductive film is provided to the anode electrode 30.

[0098] To the device (between the cathode electrode 13 and the gateelectrode 12) is applied a pulse voltage of about several tens voltageas a driving voltage V_(f), whereby a device current If and an electronemission current I_(e) are measured.

[0099] At that time, an equipotential line 32 is formed as shown in FIG.3, and the point to which the electric field is most concentrated isassumed to be a place of the electron emitting materials (carbon fibers)nearest to the positive electrode 30 shown by 33 and inside of the gap.

[0100] It is considered that electrons are emitted from the place towhich the electric field is most concentrated among the electronemitting materials positioned in the vicinity of the electricfield-concentrated point.

[0101] The I_(e) characteristic of the device was as shown in FIG. 4.

[0102] By arranging a plurality of the above electron emitting devices,a good display can be constructed.

EXAMPLES

[0103] The following will describe Examples of the invention in detail.

Example 1

[0104] Following the steps shown in FIGS. 1A to 1E, an electron emittingdevice was manufactured.

[0105] (Step 1)

[0106] After an quartz substrate used as the substrate 11 is thoroughlywashed, first, an underlying Ti having a thickness of 5 nm and Pt havinga thickness of 100 nm not shown in the Figure were continuouslyvapor-deposited onto all over the substrate by sputtering in order toform the etraction electrode 12 and the cathode electrode 13.

[0107] Next, in a photolithographic step, a resist pattern is formedusing a positive photoresist not shown in the Figure.

[0108] Then, using the above patterned photoresist as a mask, the Pt andTi layers were subjected to a dry etching using Ar gas to pattern theextraction electrode 12 and cathode electrode 13 having a gap betweenthe electrodes (gap width) of 5 μm.

[0109] (Step 2)

[0110] In a photolithographic step, a resist pattern 14 is formed usinga negative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

[0111] An ink for producing a catalyst was prepared by mixing 0.44 g oftetrakis(monoethanolamine)palladium acetate, 0.05 g of polyvinylalcohol, 25 g of isopropyl alcohol, and 1 g of ethylene glycol andmaking the whole amount 100 g by addition of water. The ink wasspin-coated onto the above TiN layer and baked at 350° C. for 30 minutesin the air, and then the resulting ink was subjected to a reductiontreatment at 600° C. in a hydrogen stream to form catalyst particles 16.When the particles were observed on a scanning electron microscope(SEM), Pd particles were formed on the TiN layer.

[0112] (Step 3)

[0113] Using a removing liquid for the resist patterned in Step 3, theconductive material layer 15 and catalyst particles 16 on the resist arelifted off together with the resist and a pattern of the conductivematerial layer 15 and catalyst particles 16 was left in a desiredregion.

[0114] (Step 4)

[0115] Subsequently, a thermal treatment was carried out in an ethylenestream. Then, when it was observed on a scanning electron microscope, itis found that a large number of carbon fibers 17 were formed.

[0116] The electron emitting device manufactured as above was placed ina vacuum apparatus 38 as shown in FIG. 3 and the apparatus wasthoroughly evacuated until the pressure reached 2×10⁻⁵ Pa by a vacuumevacuating apparatus 39. A voltage V_(a) of 10 kV is applied to thepositive electrode 30 apart from the device by H=2 mm. At that time, tothe device was applied a pulse voltage of a driving voltage V_(f) of 20V, whereby a device current I_(f) and an electron emission current I_(e)were measured.

[0117] I_(f) and I_(e) characteristics of the device were those as shownin FIG. 4. Namely, I_(e) rapidly increased from about a half of theapplied voltage and when V_(f) was 15V, an electron emission currentI_(e) of about 1 μA was observed. On the other hand, I_(f) was similarto the I_(e) characteristic but the value was found to be a valuesmaller than that of I_(e) by one order or more.

Example 2

[0118] An electron emitting device was manufactured in the same manneras in Example 1 with the exception that Step 2 was carried out asfollows, and I_(f) and I_(e) thereof were measured.

[0119] (Step 2)

[0120] In a photolithographic step, a resist pattern 14 is formed usinga negative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

[0121] An ink for producing a catalyst was prepared by mixing 0.42 g ofcobalt acetate tetrahydrate, 0.05 g of polyvinyl alcohol, 25 g ofisopropyl alcohol and 1 g of ethylene glycol and making the whole amount100 g by addition of water. The ink was spin-coated onto the TiN layerand baked at 350° C. for 30 minutes in the air. According to the abovesteps, the cobalt oxide particles are produced. Next, the conductivematerial layer 15 and oxide particles on the resist 14 are lifted offwith a peeling liquid for the resist, and then a heating process iscarried out at 600° C. in a hydrogen stream to reduce the cobalt oxideparticles to the metal cobalt particles.

[0122] When the particles were observed on a scanning electronmicroscope (SEM), Co particles were formed on the TiN layer. A heatingprocess is further carried out in an ethylene stream to produce a carbonfiber from cobalt particles. In this working example, since elution intoa peeling liquid is more suppressed by patterning the oxidized cobalt, areducing process was carried out after patterning the oxidizedparticles.

[0123] I_(f) and I_(e) characteristics of the resulting electronemitting device were those as shown in FIG. 4. Namely, I_(e) rapidlyincreased from about a half of the applied voltage and when V_(f) was15V, an electron emission current I_(e) of about 1 μA was observed. Onthe other hand, I_(f) was similar to the I_(e) characteristic but thevalue was found to be a value smaller than that of I_(e) by one order ormore.

Example 3

[0124] An electron emitting device was manufactured in the same manneras in Example 1 with the exception that Step 2 was carried out asfollows, and I_(f) and I_(e) thereof were measured.

[0125] (Step 2)

[0126] In a photolithographic step, a resist pattern 14 is formed usinga negative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

[0127] An ink for producing a catalyst was prepared by mixing 0.42 g ofnickel acetate tetrahydrate, 0.05 g of polyacrylic acid, 25 g ofisopropyl alcohol and 1 g of ethylene glycol and making the whole amount100 g by addition of water. The ink was spin-coated onto the TiN layerand baked at 350° C. for 30 minutes in the air, and then the resultingink was subjected to a reduction treatment at 600° C. in a hydrogenstream to form catalyst particles. When the particles were observed on ascanning electron microscope (SEM), Ni particles were formed on the TiNlayer.

[0128] I_(f) and I_(e) characteristics of the resulting electronemitting device were those as shown in FIG. 4. Namely, I_(e) rapidlyincreased from about a half of the applied voltage and when V_(f) was15V, an electron emission current I_(e) of about 1 μA was observed. Onthe other hand, I_(f) was similar to the I_(e) characteristic but thevalue was found to be a value smaller than that of I_(e) by one order ormore.

Example 4

[0129] An electron emitting device was manufactured in the same manneras in Example 1 with the exception that Step 2 was carried out asfollows, and I_(f) and I_(e) thereof were measured.

[0130] (Step 2)

[0131] In a photolithographic step, a resist pattern 14 is formed usinga negative photoresist to be used for subsequent lift-off of an upperlayer. Next, a TiN layer was formed as the conductive material layer 15.

[0132] An ink for producing a catalyst was prepared by mixing 0.63 g ofiron acetylacetonate and 0.06 g of polyvinylpyrrolidone and making thewhole amount 100 g by addition of ethanol. The ink was spin-coated ontothe TiN layer and subjected to a thermal treatment at 600° C. undervacuum. When the product was observed on a scanning electron microscope(SEM), Fe particles were formed on the TiN layer.

[0133] I_(f) and I_(e) characteristics of the resulting electronemitting device were those as shown in FIG. 4. Namely, I_(e) rapidlyincreased from about a half of the applied voltage and when V_(f) was15V, an electron emission current I_(e) of about 1 μA was observed. Onthe other hand, I_(f) was similar to the I_(e) characteristic but thevalue was found to be a value smaller than that of I_(e) by one order ormore.

[0134] According to the invention, catalyst particles for growing carbonfibers are obtained on a substrate without requiring any complex processand carbon fibers are satisfactorily grown from the catalyst particles.Also, the electron emitting device using the carbon fibers achieves goodelectron emitting characteristics. Moreover, according to the invention,distance between individual carbon fibers can be increased and as aresult, an electric field can be sufficiently applied to the individualcarbon fibers. Accordingly, an electron emitting device having excellentelectron emitting characteristics can be efficiently manufactured andfurthermore, a display using the electron emitting device can beefficiently provided.

What is claimed is:
 1. A method for manufacturing carbon fiber,comprising: a step of forming a coated film containing a metal organiccompound and a water-soluble polymer compound by applying an ink forproducing a catalyst comprising a solution containing at least the metalorganic compound and the polymer compound onto a substrate, a step offorming catalyst particles comprising a metal constituting said metalorganic compound by heating said coated film, and a step of formingcarbon fibers by bringing a gas containing carbon into contact with thecatalyst particles.
 2. The method according to claim 1, wherein saidpolymer compound is any one selected from the group consisting ofpolyvinyl alcohol, polyacrylic acids and polyvinylpyrrolidone.
 3. Themethod according to claim 1, wherein said metal constituting the metalorganic compound is any one selected from the group consisting of Pd,Fe, Co and Ni.
 4. The method according to claim 1, wherein said metalorganic compound is a metal organic complex.
 5. The method according toclaim 1, wherein a main solvent of said catalyst-manufacturing ink iswater.
 6. The method according to claim 1, wherein a main solvent ofsaid catalyst-manufacturing ink is an organic solvent.
 7. The methodaccording to claim 1, wherein the step of heating said coated film iscarried out in a non-oxidizing atmosphere.
 8. The method according toclaim 1, wherein the step of heating said coated film is a step ofbaking the coated film in an oxidizing atmosphere and then heating it ina reducing atmosphere.
 9. The method according to claim 1, wherein saidgas containing carbon is a hydrocarbon gas.
 10. The method according toclaim 1, wherein said gas containing carbon is a mixed gas of ahydrocarbon gas with hydrogen gas.
 11. A method for manufacturing anelectron emitting device containing carbon fibers connected to anelectrode comprising at least: a step of forming a coated filmcontaining a metal organic compound and a water-soluble polymer compoundby applying an ink for producing a catalyst comprising a solutioncontaining at least the metal organic compound and the water-solublepolymer compound onto the electrode, a step of forming catalystparticles comprising a metal constituting said metal organic compound onsaid electrode by heating said coated film, and a step of forming carbonfibers by bringing a gas containing carbon into contact with thecatalyst particles.
 12. The method according to claim 11, wherein saidpolymer compound is any one selected from the group consisting ofpolyvinyl alcohol, polyacrylic acids and polyvinylpyrrolidone.
 13. Themethod according to claim 11, wherein said metal constituting the metalorganic compound is any one selected from the group consisting of Pd,Fe, Co and Ni.
 14. The method according to claim 11, wherein said metalorganic compound is a metal organic complex.
 15. The method according toclaim 11, wherein said gas containing carbon is a mixed gas of ahydrocarbon gas with hydrogen gas.
 16. An ink for producing a catalystfor growing carbon fibers, comprising at least a metal organic compound,a water-soluble polymer compound and a solvent.
 17. Thecatalyst-manufacturing ink according to claim 16, wherein said polymercompound is any one selected from the group consisting of polyvinylalcohol, polyacrylic acids and polyvinylpyrrolidone.
 18. Thecatalyst-manufacturing ink according to claim 16, wherein said metalconstituting the metal organic compound is any one selected from thegroup consisting of Pd, Fe, Co, and Ni.
 19. The catalyst-manufacturingink according to claim 16, wherein said metal organic compound is ametal organic complex.
 20. The catalyst-manufacturing ink according toclaim 16, wherein said solvent is mainly water.
 21. Thecatalyst-manufacturing ink according to claim 16, wherein said solventis mainly an organic solvent.
 22. A method for manufacturing a displayusing a plurality of electron emitting devices, wherein said electronemitting devices are manufactured by the method according to claim 11.